1. Field of the Invention
The present invention relates to the formation of biomedical devices and, more particularly, to the use of a mold assembly for the formation of an ophthalmic device having an optical surface. The biomedical device is formed in a casting mold having an anterior mold section and a posterior mold section, wherein the mold sections can be operably engaged by an interference fit between ribs on one mold section and an annular shoulder on the second mold section. At least one of the mold sections includes an optical quality surface for imparting a corresponding optical surface on the ophthalmic device.
2. Description of Related Art
One method for making ophthalmic devices such as contact lenses is cast molding. Cast molding of contact lenses involves depositing a curable mixture of a polymerizable lens material, such as a monomer, in a casting mold cavity that is formed by at least two assembled casting mold sections; curing the mixture; disassembling the casting mold sections and removing the molded lens. Post-molding processing steps, for example, hydration in the case of hydrogel lenses, can also be employed. Representative cast molding methods are disclosed in U.S. Pat. No. 5,271,875 (Appleton et al.); U.S. Pat. No. 4,197,266 (Clark et al.); U.S. Pat. No. 4,208,364 (Shepherd); U.S. Pat. No. 4,865,779 (Ihn et al.); U.S. Pat. No. 4,955,580 (Seden et al.); U.S. Pat. No. 5,466,147 (Appleton et al.); and U.S. Pat. No. 5,143,660 (Hamilton et al.).
The configuration of the mold, and particularly the optical surfaces of the mold, at least partially determine the resulting surfaces of the lens. While a significant number of optical defects can be corrected with the molded biomedical devices, as each device typically requires two mold halves, there is a need to optimize the configuration of the casting mold.